Brief Explanation

Convenient notation for writing programs using arrows.

As this is an extension of the 'do'-notation, and as it has its own way of dealing with recursive definitions,
this is related to RecursiveDo. On the one hand, it might be that the arrow rec notation might be suitabe
for monadic recursive do as well, instead of mdo. Arguably, rec is a bit more suggestive. On the
other hand, if it is decided that the monadic do should be implicitly recursive, then it would make sense
to try to do the same for the arrow do. And if that is not possible, that could be considered an argument
against making the monadic do implicitly recursive.